Plant communities of a tussock tundra landscape in the Brooks Range Foothills, Alaska

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1 Journal of Vegetation Science 5: , 1994 IAVS; Opulus Press Uppsala. Printed in Sweden - Plant communities of a tussock tundra landscape, Alaska Plant communities of a tussock tundra landscape in the Brooks Range Foothills, Alaska Walker, Marilyn D.*, Walker, Donald A. & Auerbach, Nancy A. Institute of Arctic and Alpine Research, University of olorado, Boulder, O , USA; *Fax ; MARILYN.WALKER@OLORADO.EDU Abstract. We present the first vegetation analysis from the Arctic Foothills of northern Alaska according to the Braun- Blanquet approach. The data are from the Imnavait reek and Toolik Lake regions. We focus on associations of dry and mesic upland surfaces and moderate snow accumulation sites; other upland plant communities, i.e. those of blockfields, nonsorted circles, and water tracks, are briefly described. Summary floristic information is presented in a synoptic table. Five associations and 15 community types are tentatively placed into seven existing syntaxonomical classes. The community descriptions are arranged according to habitat: dry exposed acidic sites, moist acidic shallow snowbeds, moist non-acidic snowbeds, moist acidic uplands, and moist nonacidic uplands. Many of the communities are Beringian vicariants of associations previously described from Greenland and the European Arctic. The described communities have a widespread distribution in northern Alaska. The relationship of the associations to complex environmental gradients are analyzed using Detrended orrespondence Analysis. ommunity composition is controlled primarily by mesotopographic relationships (slope position and soil moisture), microscale disturbances, and factors related to long-term landscape evolution. Keywords: lassification; DA; Eriophorum vaginatum; Gradient analysis; Sphagnum; Syntaxonomy; Vicariant. Abbreviations: DA = Detrended orrespondence Analysis; NTR = Nomenclatural type relevé. Nomenclature: D.F. Murray, Electronic authority file, erbarium, University of Alaska, Fairbanks, AK, USA; identifications verified by David Murray (vascular taxa) and Barbara Murray (cryptogamic taxa); voucher specimens deposited at Fairbanks. Introduction Tussock tundra dominates upland arctic landscapes in Alaska, northwestern anada, and northeastern Russia (Bliss & Matveyeva 1992). The term tussock refers to the physiognomy of the tussock-forming sedge Eriophorum vaginatum. The range of E. vaginatum extends throughout the Arctic, except for the eastern half of North America and Greenland. Tussock tundra has been described in many areas of northern Alaska (e.g. anson 1951, 1953; hurchill 1955; Bliss 1956, 1962; Spetzman 1959; Douglas & Tedrow 1960; Johnson et al. 1966; Lambert 1968; D.A. Walker et al. 1982). Some of these studies have touched on the variation that occurs within tussock tundra with respect to topography, hydrology and soils, but there remains a general impression that tussock tundra is a uniform vegetation type that varies little over vast areas of the Arctic. ere we present a classification and ordination analysis of tussock tundra vegetation that accounts for some of its considerable variability, particularly along p gradients. The tussock tundra landscapes of the Toolik Lake and Imnavait reek region of Alaska s Brooks Range Foothills have been the focus of many ecosystem-level research programs over the past 20 years (e.g. Shaver et al. 1986, 1991; hapin et al. 1988; Oechel 1989; obbie et al. in press). A multiple-scale, hierarchical geographic information system (GIS) is under development for the Imnavait reek and Toolik Lake region to support ongoing projects (D.A. Walker & M.D. Walker 1991 in press). The GIS provides a regional geobotanical framework for ecosystem models, remote-sensing studies, and other studies that extrapolate key ecosystem traits, such as soil carbon, net primary production, and tracegas fluxes, to a broader region. The classification of the major vegetation types described here is used as a foundation for the vegetation map units in the GIS. This is the first application of the Braun-Blanquet approach to the vegetation of the Alaskan arctic foothills. Other vegetation analyses of the North American Arctic that have used the Braun-Blanquet approach include unpublished dissertations by Lambert (1968) and Barrett (1972), and Thannheiser s (e.g. 1976, 1987 a,b) coverage of coastal and wetland vegetation of the anadian Arctic. ooper (1986) presented a classification of the

2 844 Walker, M.D. et al. Alaska 164º 160º 156º 152º 148º 144º Barrow Beaufort Sea Prudhoe Bay ARTI OASTAL PLAIN 71º 70º Fig. 1. The North Slope of Alaska, showing major physiographic provinces and locations of Toolik Lake and Imnavait reek intensive study areas km ARTI FOOTILLS Toolik Lake Imnavait reek BROOKS Rose, Alaska Detail,11/28/94 69º vegetation of the Arrigetch reek area in the Brooks Range of Alaska, an alpine site to the south of arctic treeline. Komárková (1993, Komárková & McKendrick 1988; Komárková & Webber 1980) used the Braun- Blanquet approach to describe a wet coastal plain ecosystem at Atkasook, Alaska. Komárková s work is by far the most complete analysis of a tussock-tundra landscape, but the descriptions of the associations are not yet published. Our paper presents the first formal Braun- Blanquet descriptions from the arctic foothills. Forthcoming descriptions from Atkasook, other sites in northern Alaska, and Siberia should give a more complete picture of the regional variability of tussock tundra. Study area The study area encompasses two research sites, Toolik Lake and Imnavait reek (Fig. 1). Both sites are in the Southern Arctic Foothills physiographic subprovince of the Alaskan North Slope (Wahrhaftig 1965). The region lies north of the Brooks Range, a northwestern extension of the Rocky Mountain ordillera. It is treeless and underlain by continuous permafrost, m thick (Osterkamp & Payne 1981). The steep mountains of the Brooks Range give way abruptly to the gently-sloping Arctic Foothills, which are characterized by broad ridges, irregular buttes, mesas, and intervening rolling tundra plains (Selkregg 1975). The terrain varies in elevation from about 180 m at the northern edge of the foothills to over 1050 m, with local relief as much as 750 m, although most hills are considerably smaller. The hills are dissected by water tracks, beaded and meandering streams, and braided rivers, the majority of which flow northward toward the Beaufort Sea (D.A. Walker et al. 1989; M.D. Walker et al. 1989; D.A. Walker & M.D. Walker in press). The landscapes of the two sites are quite different due primarily to different glacial histories. The Imnavait reek site (68 37' N, ' W) is located in the headwaters of Imnavait reek, a small beaded tributary of the Kuparuk River. The site is on Sagavanirktok (mid-pleistocene) glacial drift (amilton 1986). ills around Imnavait reek are mostly gently rolling, rising less than 100 m from the valley bottoms to the ridge crests, and elongated in a NNW direction. Elevation at the site varies from about 770 m to about 980 m (D.A. Walker et al. 1989). The Toolik Lake area (68 37' N, ' W) is a younger landscape glaciated during the late Pleistocene. It includes large areas of Itkillik I (deglaciated ca yr) and Itkillik II (deglaciated about yr) glacial drifts (amilton 1986). The Toolik Lake landscape is dotted with small glacial lakes, kames, and moraines and is more heterogeneous than the Imnavait reek landscape (M.D. Walker in press). Elevations range from about 670 to 850 m. The Foothills climate has some of the warmest summer temperatures and coldest winter temperatures on the North Slope (augen 1982). Mean annual temperature ( ) at Imnavait reek is 7.5, and total mean annual precipitation ( ) is 330 mm (inzman et al. in press). The mean July air temperature is 10.9 ; the mean January temperature is a. 33 % of the total precipitation falls as snow (10.9 cm water equivalent). Snow distribution is extremely variable due to redistribution by wind, but snow depth averages ca. 50 cm prior to melt, which occurs in early to late May. Prevailing winds, especially during winter, are primarily from the south, causing deep drifts to form on north-facing slopes. ydrologic activity ceases in mid-september when the ground freezes. Because of its slightly higher elevation, snow remains at Imnavait reek a few days longer than at Toolik Lake, and foggy conditions are more common, but otherwise climate differences between the sites are small (inzman et al. in press; Arctic LTER unpubl. data). Methods Field sampling The vegetation classification is derived from 154

3 - Plant communities of a tussock tundra landscape, Alaska permanent plots, 73 at Imnavait reek and 81 near Toolik Lake. The sampling was done during the periods of 1-10 August 1984 and 17 August - 4 September 1985 at Imnavait reek and 1-26 August 1989 at Toolik Lake. We used the centralized replicate sampling procedure (Mueller-Dombois & Ellenberg 1974). Plot locations were subjectively chosen in areas of homogeneous vegetation that were representative of the major plant communities. Most vegetation plots were ca. 80 m 2, somewhat larger than the m 2 recommended for heathland samples and within the m 2 recommended for scrub communities (Westhoff & van der Maarel 1978). 21 plots contained mosaics of distinct homogeneous vegetation elements associated with microtopographic features such as frost scars, stone stripes and hummocks. In these cases, data from each element were kept separate, which increased the number of relevés by 11; thus in total 165 relevés were used. On the other hand, 11 samples were excluded from the classification because they represented ecotones, mixed communities, or single examples of non-extensive communities. All vascular, bryophyte, and lichen species were scored using the Braun-Blanquet cover-abundance scale (Mueller-Dombois & Ellenberg 1974). A small sample of each species was collected and returned to the laboratory for final identification. A soil pit was dug immediately adjacent to each vegetation sample, and the soil was described and classified to the level of subgroup using U.S. Department of Agriculture standard methods (Anon. 1975). Soil samples were collected from all horizons in a subset of plots that represented the best example of each vegetation type. For the remaining plots, a single soil sample was collected from 10 cm depth (rooting zone for most tundra species). Other physical characteristics measured for each relevé were degree of slope, aspect, and rock cover. Snow depth was measured on each plot in mid-may Percentage soil moisture was determined by drying field samples at 65 for 72 h and determining percentage weight loss. Organic matter was determined by the Walkley-Black procedure (Nelson & Sommers 1982). Particle size was determined by using sieves to separate the sand fraction (0.5-2 mm) and then separating silt and clay with the pipette method (Gee & Bauder 1986). Soil p was determined with the saturated paste method (Jackson 1958) using a hemtrix Type 400 p meter. The terms acidic and non-acidic within this paper refer to U.S. soil taxonomy nomenclature (Anon. 1975), with acidic sites having p < 5.0 and non-acidic sites having p 5.0. ations (a +2, Mg +2, K + ) were extracted using the ammonium acetate method (Thomas 1982). The filtrate was analyzed using a Perkin-Elmer atomic absorption spectrophotometer model no NO 3 was extracted with Kl (Keeney & Nelson 1982) and analyzed on a Dionex 2010i ion chromatograph (Dick & Tabatabai 1979). lassification Vegetation was classified using the Braun-Blanquet sorted-table method (Mueller-Dombois & Ellenberg 1974; Westhoff & van der Maarel 1978) and the specific protocol of Daniëls (1982) for distinguishing vegetation types. ommunity types are described as associations when we had more than 10 relevés available. All data are summarized in a synoptic table (App. 1). Individual relevé tables are presented for five formally named associations and four subassociations with the nomenclatural type relevé (NTR) indicated (Barkman et al. 1986). The faithful, differential and constant taxa comprise the set of diagnostic taxa for each community or group and forms the basis of the classification. The synoptic table presents taxa with their constancy class in each community: r, present in < 5% of records; +, 5-10 %; I, %; II, %; III, %; IV, 61 < 80 %; V, 80 %; taxa which did not reach constancy class II in at least one community, were omitted. For communities of four or fewer relevés, the actual number of occurrences is shown rather than the constancy class. Following the constancy class, the average Braun- Blanquet cover-abundance class value is shown. For the purpose of computing the average, class r was converted to 0.4, and + to 0.7. Ordination Detrended orrespondence Analysis (DA) ordination - program ANOO, ter Braak (1987); species weighted equally, detrending by segments - was used to analyze relationships between variation in vegetation and environmental variation - five aquatic samples were not included in the ordinations because they share few or no species with the terrestrial samples, and including them gives the trivial result of separating terrestrial and aquatic sites. Following the ordination of all samples, a separate ordination was done for the dry and moist uplands (93 samples vs. 160 in the all-terrestrial sample ordination) in order to better characterize relationships within that portion of the landscape. DA is based on a model of unimodal species response along gradients, and its performance at reconstructing gradients suffers when this assumption is not met, as well as from its rescaling algorithm, which somewhat arbitrarily repositions species along the gradient (Peet et al. 1988; van Groenewoud 1992). owever, DA, even if it does not perfectly reproduce complex gradients, produces first axes showing major directions of variation in the data

4 846 Walker, M.D. et al. and the relationship of the classification to major environmental gradients (Peet et al. 1988; Økland 1992). Environmental variables were related to the ordination axes with biplot diagrams, which indicate the direction in the ordination diagram that has the maximum correlation with a particular environmental variable (Dargie 1984; Jongman et al. 1987). Results: lassification The classification resulted in five associations and 15 community types that have been provisionally placed into eight Braun-Blanquet classes (Table 1). In this section we focus on the communities of dry and mesic uplands within four classes: arici rupestris-kobresietea bellardii Ohba 74, etrario-loiseleurietea Suzuki-Tokyo & Umezu in Suzuki-Tokyo 1964, Oxycocco-Sphagnetea Braun-Blanquet & Tüxen 1943 and Scheuchzerio- aricetea nigrae (Nordhagen 1936) Tüxen For each type some characteristic vascular plants, mosses and lichens will be listed (indicated with v, m and l respectively). The descriptions of the vegetation types are arranged according to habitat: - dry acidic exposed sites: Selaginello sibiricae-dryadetum octopetalae, Salici phlebophyllae-arctoetum alpinae, ierochloë alpina-betula nana comm.; - moist acidic shallow snowbeds: arici microchaetae- assiopetum tetragonae; - moist non-acidic shallow snowbeds: Dryas integrifolia- assiope tetragona comm.; - moist acidic uplands: Sphagno-Eriophoretum vaginati; - moist non-acidic uplands: Dryado integrifoliae-aricetum bigelowii. Dry acidic uplands Plant communities of dry uplands fall in two classes: arici rupestris-kobresietea bellardii, including Dryas octopetala dominated vegetation on exposed south facing slopes, and etrario-loiseleurietea dry heath communities found on somewhat less exposed rocky sites. Selaginello sibiricae-dryadetum octopetalae ass. nov. (App. 1, col. 3; Table 2, NTR: TL60). This community is dominated by the prostrate shrub Dryas octopetala ssp. octopetala, fruticose lichens, and many forbs that are locally uncommon. The association has high vascular plant and lichen diversity and relatively low moss diversity (means of 18, 22, and 5 respectively). D. octopetala is a faithful taxon - shared with the Poa glauca-arnica angustifolia comm. (App. 1, col. 2) by virtue of its high cover and constancy; Selaginella sibirica has a relatively low cover but is highly faithful to the association. Other faithful taxa are: Antennaria alpina v Alectoria nigricans l Melanelia septentrionalis v Arctoparmelia separata l Minuartia obtusiloba v oelocaulon aculeatum l Oxytropis bryophila v ypogymnia subobscura l Smelowskia calycina v; Ochrolechia upsaliensis l. Other common taxa include: Anemone drummondii v Polytrichum strictum m Artemisia arctica ssp. arctica v Rhytidium rugosum m; arex rupestris v Alectoria ochroleuca l Kobresia myosuroides v Asahinea chrysantha l Salix phlebophylla v; Bryocaulon divergens l etraria spp. l. Typical microsites of this association include acidic, south-facing rocky hillslopes of kames, moraines, and sandstone outcrops. A somewhat depauperate version of the association occurs on rocky glacial outwash deposits. The sites are extremely windblown due to southerly wintertime katabatic winds blowing out of the Brooks Range; no snow was recorded on any of the permanent plots of this association in early May 1994, and similar snow distribution patterns have been observed in other years. The mean p of the 11 samples in this association is 4.7 ± 0.2. The soils thaw to depths > 100 cm by late summer. Soil organic matter content (5.5 ± 0.5 %) and available NO 3 -N (4.5 ± 0.5 ppm) are low. Dryas is the main vascular genus typifying dry sites throughout the Arctic, and it becomes more common at higher latitudes, where moisture is more limited (Rønning 1965; Barrett 1972; Yurtsev 1974; Aleksandrova 1980). In the Toolik Lake and Imnavait reek region Dryas octopetala occurs on both acidic and non-acidic substrates and Dryas integrifolia occurs on non-acidic soils. In the Brooks Range, ooper (1986) reported D. octopetala ssp. alaskensis as limited primarily to limestone areas; Elvebakk (1982) reported D. octopetala ssp. octopetala on Svalbard associated with soil p between 5.5 and 8.0, but most abundant at p > 7.0. In Fennoscandia, Dryas-dominated communities have been described from circumneutral to basic windblown sites (Nordhagen 1928; Rønning 1965). Lambert (1968), however, characterized D. octopetala in NW anada as circumneutral to slightly acidic, while our data indicate that D. octopetala occurs primarily on acidic soils with relatively low available calcium (compared to D. integrifolia). Also, D. integrifolia is found from dry sites to moderately deep snowbeds, whereas D. octopetala occurs on sites with thin or no snow cover. Thus, there is apparently geographic variation in how these species respond to substrate chemistry and snow depth. The syntaxonomic status of Dryas-dominated types, because of the taxonomic complexity of the genus Dryas, has also been in contention. Dierßen (1992) placed Dryas octopetala types in the aricion nardinae Nordhagen 1935 and Dryas integrifolia types in the Dryadion integrifoliae (Ohba 1974) Daniëls 1982.

5 - Plant communities of a tussock tundra landscape, Alaska Table 1. Tentative class, community and association names, and habitats of the Imnavait reek and Toolik Lake region. Rhizocarpetea geographici etraria nigricans-rhizocarpon geographicum comm. arici rupestris-kobresietea bellardii Poa glauca-arnica angustifolia comm. Selaginello sibiricae-dryadetum octopetalae Dryas integrifolia-assiope tetragona comm. etrario-loiseleurietea arici microchaetae-assiopetum tetragonae Salici phlebophyllae-arctoetum alpinae ierochloë alpina-betula nana comm. Oxycocco-Sphagnetea Sphagno-Eriophoretum vaginati Sphagnum lenense-salix fuscescens comm. Scheuchzerio-aricetea nigrae Dryado integrifoliae-aricetum bigelowii Tomentypnum nitens-trichophorum caespitosum comm. Sphagnum orientale-eriophorum scheuchzeri comm. Eriophorum angustifolium-arex aquatilis comm. arex aquatilis-arex chordorrhiza comm. ippuris vulgaris-arctophila fulva comm. Potametea ippuris vulgaris-sparganium hyperboreum comm. Betulo-Adenostyletea Salix alaxensis-salix lanata comm. Eriophorum angustifolium-salix pulchra comm. Salicetea herbaceae Salix rotundifolia comm. Anthelia juratzkana-juncus biglumis comm. Xeric, acidic, sandstone and conglomerate glacial erratics, and blockfields Subxeric, exposed, non-acidic, animal dens, with deep rich soils Xeric, very exposed, acidic, rocky, south-facing slopes of kames, moraines, and sandstone outcrops Subxeric, well-drained, non-acidic, shallow snowbeds Subxeric, well drained, acidic shallow snowbeds Subxeric, moderately exposed, acidic, rocky sites Subxeric, somewhat protected, acidic sites Mesic to subhygric, acidic, uplands, moderate snow Subhygric, acidic, hummocks, in poor fens Mesic to subhygric, non-acidic, uplands and hummocks in fens Subhygric, non-acidic hummocks in fens ygric, acidic, poor fens ygric, non-acidic, fens Subhygric to hygric, non-acidic fens ydric, marshes, pond margins ydric, beaded ponds, oxbow lakes Subhygric to subxeric, non-acidic, riparian margins, river bars Subhygric to hygric, non-acidic hillslope watertracks Mesic, non-acidic, deep snowbeds Subxeric, acidic, nonsorted circles. Salici phlebophyllae-arctoetum alpinae ass. nov. (App. 1, col. 6; Table 3, cols , NTR: TL71) Dry shallow snow accumulation sites support stands dominated by prostrate ericaceous species and fruticose lichens. The community has relatively low vascular plant and bryophyte diversity and high lichen diversity (mean of 10, 5, and 19 respectively). The dwarf shrub Arctous alpina is the sole faithful taxon of this association based on its high constancy and abundance. Other common dwarf shrubs include Salix phlebophylla, Vaccinium uliginosum and V.vitis-idaea, any of which can be dominant. Bistorta plumosa and ierochloë alpina are also common. ommon lichens and mosses include: Bryocaulon divergens m ladina rangiferina l Dicranum spp. m ladonia pyxidata l Polytrichum strictum m;. macrophylla l etraria cucullata l. uncialis l. islandica l Dactylina arctica l. nivalis l Sphaerophorus globosus l ladina arbuscula l Thamnolia spp. l. This is a common association of dry, leached, rocky sites with shallow winter snow cover, such as on moderately windblown glacial outwash deposits, kames, and moraines. Typical microsites are very shallow depressions and areas with somewhat more snow than the very windblown Selaginello sibiricae-dryadetum octopetalae (mean of 5 ± 2 cm). The soils are only somewhat more organic-rich (9.1 ± 2.8 %), and the soil NO 3 -N values are very low, 2.2 ± 0.5 ppm. The mean soil p of the 12 samples is 4.0 ± 0.1. This is apparently a Beringian association, which may represent a vicariant of Arctostaphylo-Alectorietum octopetalae Du Rietz We included Salix phlebophylla in the name as an area differential taxon for Beringia. Associations of Arctous alpina and ierochloë alpina have been reported from other areas in Alaska (hurchill 1955), from the Foothills zone of northern anada (Lambert 1968), and from low arctic tundra of Siberia (Aleksandrova 1980). ierochloë alpina-betula nana comm. (App. 1, col. 7) This community is dominated by dwarf and low shrubs and fruticose lichens. It is floristically poorly characterized, but Betula nana reaches its maximum abundance here and defines the community. Pedicularis labradorica is a potential diagnostic taxon, with a low presence in other local communities. onstant taxa are:

6 848 Walker, M.D. et al. Table 2. Selaginello sibiricae-dryadetum octopetalae. Reference no. 1 = relevé I58A, 2 = I54, 3 = I53, 4 = I52, 5 = TL60 = NTR, 6 = TL47, 7 = TL07, 8 = TL18, 9 = I33, 10 = I42, 11 = TL46. Reference no Number of vascular taxa Number of bryophyte taxa Number of lichen taxa Total number of taxa Faithful and differential taxa shared with the Poa glauca-arnica angustifolia comm.: Dryas octopetala var. octopetala Selaginella sibirica r1. Minuartia obtusiloba Bupleurum triradiatum ssp. arcticum..+1++r+.+. arex rupestris Anemone drummondii Encalypta rhaptocarpa Poa glauca Arnica angustifolia ssp. angustifolia Faithful and differential taxa of the association: Polytrichum piliferum ypogymnia subobscura Antennaria alpina var. media Alectoria nigricans Oxytropis bryophila Ochrolechia upsaliensis Arctoparmelia separata etraria nigricans oelocaulon aculeatum.++.+.r.+.. Melanelia septentrionalis Smelowskia calycina onstants: Bryocaulon divergens Thamnolia subuliformis+vermicularis etraria cucullata etraria nivalis Asahinea chrysantha Alectoria ochroleuca Salix phlebophylla..+11+r+12+ Sphaerophorus globosus etraria islandica Stereocaulon alpinum+tomentosum ierochloë alpina ladonia amaurocraea Peltigera aphthosa +r.+.+r.++. Other taxa: Rhytidium rugosum ladonia uncialis Artemisia arctica ssp. arctica...11+r.r+. Peltigera canina..++++r...+ Vaccinium vitis-idaea ssp. minus...r+112 Dicranum elongatum+groenlandicum Polytrichum strictum Masonhalea richardsonii...+..r.+1+ Kobresia myosuroides ladina arbuscula Pertusaria dactylina Saxifraga nivalis Pedicularis capitata Psoroma hypnorum Saxifraga bronchialis ssp. funstonii.r ierochloë alpina v Dicranum spadiceum m Ledum decumbens v ylocomium splendens m Aulacomnium turgidum m Masonhalea richardsonii m Other common taxa include: Bistorta plumosa v ladina arbuscula l etraria cucullata l ladonia amaurocraea l. islandica l Sphaerophorus globosus l. The community is found in dry, somewhat protected sites such as depressions or the lee of larger rocks on till deposits, and in the troughs of rocky high-centered polygons on glacial outwash deposits. Snow, which was on average 32 cm deep in 1994, is deeper than in the Salici phlebophyllae-arctoetum alpinae, but somewhat shallower than in the snowbed association arici microchaetae-assiopetum tetragonae. Soil p is very Additional taxa with three or less occurrences: I58A: etraria commixta 1, Douglasia ochotensis +, Racomitrium lanuginosum +; I54: arex obtusata +, atapyrenium lachneum +, Dicranum muehlenbeckii +, Douglasia ochotensis +, Lecanora epibryon 1, Rinodina turfacea +, Saxifraga tricuspidata +, Solorina bispora +; I53: Erigeron muirii +, Eritrichum aretioides +, Phlox sibirica ssp. sibirica +, Pogonatum urnigerum 1, Potentilla uniflora +, Pseudephebe pubescens +, Senecio atropurpureus ssp. frigidus r, Sphaerophorus fragilis +; I52: Arnica lessingii 1, aloplaca jungermanniae +, arex obtusata +, ladonia pyxidata +, Phlox sibirica ssp. sibirica +, Potentilla uniflora +, Saxifraga tricuspidata +, Trisetum spicatum +; TL60: Aconitum delphinifolium ssp. paradoxum r, Androsace chamaejasme ssp. lehmanniana +, Arnica griscomii ssp. frigida +, Arthrorhaphis alpina +, Bryoerythrophyllum recurvirostre +, Buellia papillata +, aloplaca jungermanniae +, arex capillaris +, ladina rangiferina +, ladonia macrophylla +,. pocillum +, Festuca altaica +, Gastrolychnis affine +, Minuartia arctica +, Ochrolechia frigida +, Oxytropis campestris s.l. 1, Pertusaria bryontha +, Potentilla nivea +, Rhododendron lapponicum +, Saxifraga hieracifolia +, S. reflexa +, S. tricuspidata +, Tortella fragilis 1, Zygadenus elegans +; TL47: Bistorta vivipara r, alamagrostis purpurascens +, arex capillaris +, ladonia pyxidata +,. subfurcata +, Erigeron hyperboreus +, Festuca baffinensis +, Lecanora epibryon +, Luzula confusa r, Nephroma expallidum +, Oxytropis campestris s.l. +, O. maydelliana +, Pedicularis lanata +, Poa arctica +, P. lanata +, Racomitrium lanuginosum +, Radula prolifera +, Thalictrum alpinum +, Tortella fragilis +; TL07: Androsace chamaejasme ssp. lehmanniana +, Arnica lessingii +, arex capillaris r,. microchaeta r, ladonia coccifera +, Dryas integrifolia +, Festuca baffinensis +, Gymomitrion coralloides +, Lecanora epibryon +, Luzula confusa r, L. multiflora r, Ochrolechia frigida +, Pohlia nutans + Potentilla nivea +, Saxifraga hieracifolia r, Vaccinium uliginosum r; TL18: Alectoria minuscula +, Anastrophyllum minutum +, Androsace chamaejasme ssp. lehmanniana +, Oxytropis arctica +, Pedicularis lanata +, Pertusaria panyrga +, Polytrichum hyperboreum +, Saxifraga reflexa +, Stereocaulon condensatum +, Tritomaria quinquedentata +; I33: Arctous alpina +, Arnica griscomii ssp. frigida +, Bryum algovicum +, arex microchaeta +,etraria andrejevii +, ladonia alaskana 1,. pocillum +, Dactylina arctica +, Dicranum acutifolium +, Empetrum hermaphroditum 1, Encalypta brevicolla +, Minuartia arctica r, Pertusaria bryontha +, Polytrichum hyperboreum +; I42: Bistorta plumosa r, arex microchaeta +, ladina rangiferina +, ladonia coccifera +,. gracilis +, Dactylina arctica +, Encalypta brevicolla +, Lecidoma demissa +, Lobaria linita +, Mycoblastus sanguinarius +, Nephroma expallidum +, Pedicularis langsdorffii +, Poa arctica +, Polytrichum hyperboreum 1, Vaccinium uliginosum +; TL46: Anastrophyllum minutum +, Arctous alpina 2, Aulacomnium turgidum +, Barbilophozia barbata +, Bistorta plumosa +, alamagrostis inexpansa +, assiope tetragona ssp. tetragona +, ladina rangiferina +, ladonia chlorophaea +,. coccifera +,. deformis r,. gracilis +,. pyxidata +,. subfurcata +, Dactylina arctica +, Diapensia lapponica ssp. obovata 1, ypnum bambergeri +, Luzula confusa +, L. multiflora +, Novosieversia glacialis r, Ochrolechia frigida +, Oxytropis maydelliana 1, Pedicularis lanata +, Poa lanata +, Saussurea angustifolia +, Saxifraga nelsoniana r, Stellaria longipes +, Tofieldia coccinea +, Vaccinium uliginosum 2. low, 3.8 ± 0.2. Soil organic matter and available nitrate are the highest of any of the communities on dry sites, 39 ± 14 % and 17 ppm respectively. The community appears to be related to the Empetro- Betuletum nanae Nordhagen 1943, which is recognized by the abundance of Betula nana, scarcity of higher plants, the predominance of fruticose lichens, and near absence of pleurocarpous mosses. The ierochloë alpina-betula nana comm. is somewhat moister and has a better developed moss carpet than the Empetro- Betuletum nanae. Moist acidic shallow snowbeds arici microchaetae-assiopetum tetragonae ass. nov. (App. 1, col. 5; Table 3, cols. 1-13, NTR: I41). This association is dominated by dwarf shrubs and fruticose lichens. Its relevés have a relatively high diversity - 19 vascular plants, 9 mosses and 18 lichens. Diapensia lapponica ssp. obovata and uperzia selago ssp. appressa are faithful taxa. onstant taxa are: Betula nana ssp. exilis v Pyrola grandiflora v; arex microchaeta v Aulacomnium turgidum m assiope tetragona v ylocomium splendens m; Ledum palustre ssp. decumbens v Nephroma arcticum l. Other common taxa include: Salix phlebophylla v Peltigera aphthosa l Vaccinium uliginosum v Thamnolia spp. l. V. vitis-idaea v;

7 - Plant communities of a tussock tundra landscape, Alaska This association occurs in moderately deep snowbeds (mean snow depth in 1994: 57 ± 13 cm) on acidic substrates. The best developed stands occur on steep northfacing, well-drained slopes, protected from winds and extreme sun with over 100 cm of snow. Poorly developed stands occur on acidic non-sorted stripes on the shoulder of some hill slopes with shallow snow drifts Soil p is 4.4 ± 0.2, and the soils are organic-rich (29.6 ± 5%) mineral soils with moderate NO 3 -N (12 ± 7 ppm). Soil moisture is moderate and variable (84 ± 25 %). This association appears to be a western North American vicariant of the assiopetum tetragonae (Böcher 1933) Daniëls 1982, which has an eastern North America- Greenland distribution. Area-differential taxa for the Alaska association include: Artemisia arctica ssp. arctica v Salix phlebophylla v Bistorta plumosa v S. pulchra v arex microchaeta v S. reticulata v Pedicularis langsdorfii v S. rotundifolia v Petasites frigidus v Saxifraga punctata v. Moist non-acidic shallow snowbeds Dryas integrifolia-assiope tetragona comm. (App. 1, col. 4) This community is the non-acidic counterpart to Ass. arici microchaetae-assiopetum tetragonae. assiope tetragona is the clear dominant but Dryas integrifolia is also constant and abundant. Evergreen dwarf shrubs and lichens dominate the community, and there is also a well-developed moss carpet. In addition to the taxa it shares with the Dryado integrifoliae-aricetum bigelowii, this community has the following faithful taxa: Astragalus umbellatus v Radula prolifera v Equisetum scirpoides v Silene acaulis v. Novosieversia glacialis v The many constant taxa include: Bistorta plumosa v ypnum bambergeri m arex scirpoidea v Ptilidium ciliare m Dryas integrifolia v Rhytidium rugosum m; Papaver macounii v Alectoria ochroleuca l Parrya nudicaulis v Asahinea chrysantha l Pedicularis oederi v etraria cucullata l Salix arctica v. nivalis l Salix reticulata v; ladonia amaurocraea l Aulacomnium turgidum m. gracilis l Dicranum angustum m Dactylina arctica l. The best developed stands of this community occur on steep north-facing slopes with over 100 cm of snow and non-acidic soils (p 5.8 ± 0.1). This community also occurs on east and west-facing slopes where smaller snowdrifts form. It is normally not found on south-facing slopes due to the prevailing winds which sweep these slopes of snow. The mean measured snow depth in 1994 was 32 ± 19 cm. Soil organic matter is high (46 ± 9 %) as is calcium (41 meq/100 g). Available NO 3 -N is surprisingly low (8.6 ppm). This community is a Beringian vicariant of the Dryado-assiopetum (Fries 1913) adaã 1946, described from the Eurosiberian Arctic (Dierßen 1992). Similar communities have been described from the snowbeds at Prudhoe Bay (D.A. Walker 1985; D.A. Walker & Everett 1991) and pingos on the eastern Arctic oastal Plain of Alaska (M.D. Walker 1990). Razzhivin ( this issue) describes a similar provisional association from hukotka. Sphagno-Eriophoretum vaginati ass. nov. (App. 1, ref. 8; Table 5, NTR I03) This is the zonal vegetation of mesic, acidic slopes throughout the Arctic Foothills. The tussock-forming sedge Eriophorum vaginatum is a conspicuous dominant in most stands, although other sedges and deciduous shrubs can be dominant. There are no truly faithful taxa for the association. Nearly all the taxa are shared with other mire communities within the class. onstant taxa include: Betula nana ssp. exilis v Sphagnum angustifolium m Bistorta plumosa v S. balticum m arex bigelowii v S. girgensohnii m assiope tetragona v S. rubellum m; Empetrum hermaphroditum v etraria cucullata l Ledum palustre ssp. decumbens v. islandica l Pedicularis lapponica v ladina arbuscula l Petasites frigidus v;. rangiferina l Anastrophyllum minutum m ladonia amaurocraea l Aulacomnium turgidum m. gracilis l Dicranum angustum m Dactylina arctica l D. groenlandicum m Peltigera aphthosa l. This association covers gentle poorly drained acidic slopes in the foothills. Gravimetric soil moisture is high (319 ± 48 %). The soils are relatively fine-grained compared to other vegetation types (41 ± 5 % silt, 42 ± 5 % clay), probably due to their occurrence on relatively stable older slopes. The average soil p is 4.6 ± 0.1. Most soils have thin (15-25 cm) surficial organic horizons above a gleyed mineral horizon. The organic content at 10-cm depth averages 54 ± 6 %, and NO 3 -N is moderate (18 ± 3 ppm). Winter snow cover tends to be moderate (32 ± 8 cm). The combination of shallow depth of thaw (36 ± 3 cm) and high water holding capacity of the Sphagnum mosses tends to promote presence of numerous hygrophytic species that would normally not be present on upland surfaces. Non-sorted circles are an important component of nearly all upland surfaces. The communities found on these features (see below) form a fine scale mosaic with the Sphagno-Eriophoretum vaginati. Vegetation dominated by E. vaginatum and. bigelowii is found throughout Alaska and east to the Mackenzie River, and in Siberia from hukotka west to

8 850 Walker, M.D. et al. Table 3. arici microchaetae-assiopetum tetragonae and Salici phlebophyllae-arctoetum alpinae. Reference no. 1 = TL08, 2 = TL19, 3 = I29A, 4 = I30A, 5 = I32A, 6 = I44A, 7 = I57, 8 = I56, 9 = I55, 10 = I40, 11 = I41 = NTR, 12 = TL49, 13 = TL50. Reference no. 14 = I38, 15 = TL05, 16 = TL71 = NTR, 17 = I09, 18 = I28, 19 = TL63, 20 = TL65, 21 = TL69, 22 I39, 23 I43, 24 = I60, 25 = I51. arici-assiopetum Salici-Arctoetum Reference no Number of vascular taxa Number of bryophyte taxa Number of lichen taxa Total number of taxa Faithful and differential taxa of the arici microchaetae-assiopetum tetragonae: assiope tetragona ssp. tetragona r ylocomium splendens Aulacomnium turgidum Diapensia lapponica ssp. obovata Ledum palustre ssp. decumbens Betula nana ssp. exilis r Racomitrium lanuginosum Peltigera aphthosa Pedicularis langsdorffii r...+ Nephroma arcticum uperzia selago ssp. appressa.r r+.... Pyrola grandiflora Bistorta vivipara Petasites frigidus Salix pulchra Senecio atropurpureus ssp. frigidus handonanthus setiformis Psoroma hypnorum Faithful and differential taxa of the Salici phlebophyllae-arctoetum alpinae: Arctous alpina ierochloë alpina Polytrichum piliferum ladonia pyxidata ladonia macrophylla onstants: Vaccinium vitis-idaea ssp. minus Thamnolia subuliformis +vermicularis etraria cucullata ladonia gracilis Masonhalea richardsonii etraria islandica ladonia amaurocraea ladina arbuscula Dicranum elongatum +groenlandicum ladina rangiferina Stereocaulon alpinum+tomentosum Dactylina arctica Bistorta plumosa r+1.++ Vaccinium uliginosum r r3++33 etraria nivalis Polytrichum strictum Sphaerophorus globosus Alectoria ochroleuca arex microchaeta r.++r+++1. Salix phlebophylla ladonia uncialis Other taxa: Asahinea chrysantha r Bryocaulon divergens alamagrostis inexpansa ladonia coccifera ladonia pleurota Pedicularis capitata.r Anastrophyllum minutum Dicranum acutifolium Pertusaria dactylina Artemisia arctica ssp. arctica r Empetrum hermaphroditum Rhytidium rugosum etraria kamczatica Loiseleuria procumbens Alectoria nigricans ladina mitis ladonia chlorophaea Luzula confusa...r Peltigera canina r... Pertusaria panyrga Saxifraga nelsoniana r. arex bigelowii r... etraria andrejevii etraria nigricans Dicranum scoparium Lophozia guttulata Table 3. (cont.) arici-assiopetum Salici-Arctoetum Reference no Pohlia nutans Salix reticulata ssp. reticulata Salix rotundifolia ssp. rotundifolia Stellaria longipes Additional taxa with three or less occurrences: TL08: oleocaulon aculeatum r, Ochrolechia frigida +, Orthilia secunda ssp. obtusata +, Sphagnum rubellum+warnstorfii +; TL19: Anemone parviflora +, Arnica lessingii +, Bupleurum triradiatum ssp. arcticum r, Bryoerythrophyllum recurvirostre +, arex capillaris +,. scirpoidea +, ladonia acuminata +, Dicranum undulatum +, Dryas integrifolia +, D. octopetala var. octopetala +, Equisetum scirpoides +, ypogymnia physodes +, Nephroma expallidum +, Novosieversia glacialis +, Oxytropis arctica r, Pedicularis labradorica +, Salix glauca +, S. chamissonis r, Silene acaulis +, Tofieldia pusilla +; I29A: Arnica lessingii +, Dicranum muehlenbeckii 3, Solorina crocea +; I30A: Arnica lessingii +, Blepharostoma trichophyllum ssp. brevirete +, Dicranum muehlenbeckii 1, Peltigera scabrosa +, Solorina crocea +, Stereocaulon paschale +; I32A: Arnica griscomii ssp. frigida +, etraria laevigata +, Dicranella varia +, Salix chamissonis +; I44A: Eriophorum triste +, Polytrichum commune 1, Sphagnum lenense +; I57: Andromeda polifolia 1, Blepharostoma trichophyllum ssp. brevirete +, ladina stellaris 1, Dactylina ramulosa +, Diplophyllum plicatum +, Luzula arctica +, Novosieversia glacialis 1, Parrya nudicaulis s.l. +, Poa alpigena +, Pogonatum urnigerum 1, Sanionia uncinata +, Sphagnum aongstroemii +, S. girgensohnii 1, S. teres 1; I56: arex misandra +, Dactylina ramulosa +, Gymnomitrion concinnatum +, Luzula arctica 1, Parrya nudicaulis s.l. +, Poa arctica +, Pogonatum urnigerum 1, Ptilium crista-castrensis +, Sanionia uncinata +, Sphagnum aongstroemii +, S. teres +, Tomentypnum nitens +; I55: Dactylina ramulosa +, Dicranum muehlenbeckii 2, Nephroma expallidum +, Papaver macounii +, Politrichastrum alpinum 1, Pogonatum urnigerum 1, Saxifraga bronchialis ssp. funstonii +, Sphagnum girgensohnii 1; I40: Dactylina beringica +, Dicranum angustum +, Gentiana glauca +; I41: Abietinella abietina 1, Arnica griscomii ssp. frigida +, Astragalus umbellatus +, Dactylina beringica r, Peltigera leucophlebia r, Poa arctica +, Politrichastrum alpinum 1, Ptilidium ciliare 1, Ptilium crista-castrensis +, Salix chamissonis 2, Tomentypnum nitens 1; TL49: arex scirpoidea +, Dicranum spadiceum 3, Equisetum scirpoides +, Minuartia arctica r, Novosieversia glacialis +, Orthilia secunda ssp. obtusata +, Pohlia cruda +, Saussurea angustifolia +, Silene acaulis +; TL50: Arnica angustifolia ssp. angustifolia +, Aulacomnium palustre 2, Boykinia richardsonii 2, ardamine digita +, arex scirpoidea +, Dicranum angustum 2, D. spadiceum 2. Equisetum arvense +, Luzula arctica +, L. multiflora r, Parnassia palustris r, Parrya nudicaulis s.l. +, Plagiomnium ellipticum +, Sanionia uncinata 2, Saussurea angustifolia +, Saxifraga nivalis +, Sphagnum rubellum+warnstorfii 1, Tofieldia pusilla r, Tomentypnum nitens 1; I38: Arctoparmelia separata +, Polytrichum hyperboreum 1, Tortula ruralis 1; TL05: ladonia ecmocyna +,. pocillum +, ypogymnia physodes 1, Melanelia septentrionalis +, Pedicularis lanata r; TL71: eratodon purpureus r; I09: eratodon purpureus +, Eriophorum vaginatum +, Lecidoma demissa +, Tritomaria quinquedentata +; I28: Arctoparmelia separata +, Asahinea scholanderi +, alliergon stramineum +, ypogymnia subobscura 1, Pseudephebe pubescens 2, Sphaerophorus fragilis 1; TL63: Ochrolechia frigida +, Peltigera malacea +, Poa alpina +; TL65: alamagrostis canadensis s.l. 1, Pedicularis labradorica +; I39: ladonia cornuta +, Polytrichum hyper- boreum +, Rubus chamaemorus +, Tetraplodon pallidus r; I43: Dactylina beringica +, Peltigera malacea +, Polytrichum hyperboreum +; I60: etraria tilesii +, ladonia alaskana +, Dryas octopetala var. octopetala 2, Festuca altaica +, Kobresia myosuroides +, Poa glauca +, P. lanata +, Saxifraga nivalis r; I51: Dryas octopetala var. octopetala +, Peltigera malacea 1. the Taymyr and Yamal peninsulas (Aleksandrova 1980). owever, only in unglaciated Alaska and hukotka is this the predominant association of the uplands. Komárková & McKendrick (1988) recognized a preliminary class (not yet formally described) of upland vegetation characterized by E. vaginatum and Ledum decumbens. Lambert (1968) described a Betulo-Eriophoretum vaginati from the western anadian Arctic, and although his stands were characterized by Betula glandulosa rather than B. nana, the floristic similarity between the anadian communities and this association is high (61%). Sphagno-Eriophoretum vaginati typicum subass. nov. (Table 4 cols. 1-26, NTR: TL54) In the typical subassociation sedges and dwarf shrubs are dominant in the overstory and mosses in the understory. In wetter microsites, the deciduous shrubs Salix pulchra or Betula nana can be > 50 cm tall and become dominant, but sedges remain an important component of the canopy. Eriophorum vaginatum may be replaced by arex bigelowii in some areas. In snowy

9 - Plant communities of a tussock tundra landscape, Alaska microsites, the evergreen shrub assiope tetragona is an important subdominant. E. vaginatum tends to be dominant on stable sites where there is no flowing water. Shrubs become more important in poorly defined ephemeral water tracks. Total species diversity of the subassociation is relatively high (mean of 41 taxa; 15 vascular plants, 14 mosses and 10 lichens). E. vaginatum, assiope tetragona, Pyrola grandiflora and Saxifraga nelsoniana are differential against the betuletosum nanae. We recognize a arex bigelowii facies of the subassociation (Table 4, cols ) that occurs on somewhat unstable slopes, often in conjunction with solifluction features. ere, E. vaginatum is absent or has a low cover in these areas. Sphagno-Eriophoretum vaginati betuletosum nanae subass. prov. (Table 4, cols , NTR: TL36) This is a well-defined low-shrub community dominated by Betula nana ssp. exilis that is common along the margins of water tracks and on palsas and high-centered polygons in colluvial basins. There is often a deep moss mat, and summer thaw commonly does not penetrate to the mineral soil horizon. Sphagnum teres is a differential taxa against the subass. typicum. ommon taxa with high cover include Aulacomnium turgidum, Ledum palustre ssp. decumbens and Rubus chamaemorus and a suite of Sphagnum species. Species diversity is somewhat less than in the typical subassociation with 12 vascular plants, 14 bryophytes, and 7 lichens. The subassociation contains most of the faithful and constant taxa but is missing Eriophorum vaginatum in most stands. Moist non-acidic uplands Dryado integrifoliae-aricetum bigelowii ass. nov. (App. 1, col. 10; Table 5, cols. 1-14, NTR: TL43) This is the non-acidic counterpart to the Sphagno- Eriophoretum vaginati, occurring on circumneutral mesic uplands and hillslopes, and limited to younger landscapes. Sedges and dwarf shrubs are dominant, and there is a well developed moss layer. Species diversity is high (26 vascular plants, 16 bryophytes, 14 lichens; total 55). The minerotrophic moss Tomentypnum nitens is constant and abundant. Faithful taxa are: Anemone parviflora v Pyrola grandiflora v Eriophorum triste v Senecio resedifolius v; Eutrema edwardsii v Aulacomnium acuminatum m Orthilia secunda ssp. obtusata v Meesia uliginosa m. onstant taxa include: Arctous rubra v atoscopium nigritum m Bistorta vivipara v Dicranum spadiceum m Pedicularis lanata v Rhytidium rugosum m; Rhododendron lapponicum v etraria islandica l Salix arctica v ladina arbuscula l Vaccinium uliginosum v; ladonia amaurocraea l Aulacomnium turgidum m. pyxidata l. This association occurs on mid to upper non-acidic slopes, primarily in younger landscapes. Gravimetric soil moisture is high, 381 ± 29 %, similar to that of the Sphagno-Eriophoretum vaginati. Soils are relatively coarse-grained (57 ± 4 % sand, 38 ± 2 % silt, and 6 ± 2 % clay). Average soil p is 6.3 ± 0.1, compared to only 4.6 for the Sphagno-Eriophoretum vaginati. Organic content of the soil is 66 ± 5 %, and NO 3 -N is low (9 ± 1 ppm). Snow depth averaged 32 ± 19 cm in This association is placed in the Scheuchzerio- aricetea nigrae, which includes the more basiphytic communities of mires and mineral-rich and moss-rich communities on poorly drained slopes. Within the class, it has affinities to the Tofieldietalia Preising in Oberdorfer Dryado integrifoliae-aricetum bigelowii caricetosum membranacae subass. nov. (Table 5, cols. 1-7, NTR: TL43). This subassociation is differentiated by Alectoria ochroleuca, Anemone parviflora, Bryum pseudotriquetrum, arex membranacea and Eriophorum vaginatum. It occupies upper mesic slope positions including the dry element of non-sorted stripes. Dryado integrifoliae-aricetum bigelowii equisetosum arvensis subass. nov. (Table 5, cols. 8-14, NTR: TL45). This subassociation is easily recognized by the abundance of Equisetum arvense, which gives the community a distinctive light green coloration in midsummer. It is differentiated by yrtomium hymenophyllum, Equisetum scirpoides, Luzula arctica, Meesia uliginosa and Petasites frigidus. The community is characteristically found on lower somewhat less stable slopes, often in areas of high snow cover. Other important communities of uplands Blockfields and glacial erratics: etraria nigricans- Rhizocarpon geographicum community (App. 1, col. 1). Two relevés collected from these sites contained many epilithic cryptogams that are typical of most glacial erratics and blockfields in the region, including: handonanthus setiformis m; Parmelia omphalodes l Alectoria nigricans l Porpidea flavocaerulescens l Arctoparmelia centrifuga l Rhizocarpon geographicum l etraria nigricans l Umbilicaria proboscidea l. The stoney glacial till and outwash deposits of the region contain many blockfields that are not covered by soil and vascular plants. Blockfields are less common on the older surfaces, but occasional glacial erratics protrude above the colluvium and peat. Most of the rocks in the region are composed of Kanayut Sandstone (amilton 1986).